Development of a fluidized bed thermogravimetric analyzer

A new fluidized bed thermogravimetric analyzer (FB‐TGA) was developed that introduces two major particularities: the pseudo variation of the weight of the reactor and the special strategy for gas flow rate adjustment according to temperature. A momentum balance was performed on the reactor and the pseudo variation of the reactor weight was evaluated by measuring the pressure drop through the gas distributor and filter. The real weight loss of the reactor was obtained by subtracting the pseudo variation of the weight from the total weight loss measured by the load cell. In addition, a special program for the gas flow rate as a function of temperature was developed and used; so the minimum fluidization regime is maintained throughout all of the experiments. The validation test of the FB‐TGA was carried out on calcium hydroxide decomposition, and the results were compared with those obtained from the conventional TGA. Diffusion control was suppressed by the application of the FB‐TGA, which was confirmed by the x‐ray diffraction analysis on the treated samples. © 2014 American Institute of Chemical Engineers AIChE J, 61: 84–89, 2015     

微型流化床与热重测定煤焦非等温气化反应动力学对比

利用微型流化床反应分析仪(MFBRA)和热重分析仪(TGA)比较煤焦与CO₂的非等温气化反应特性,并利用单一升温速率法和组合升温速率法计算反应动力学数据。结果表明:升温速率对半焦非等温气化过程有重要影响,随着升温速率的增大,起始反应温度和最大反应速率对应的气化温度增加,同一气化温度下的碳转化率降低,而且利用单一升温速率法求取气化反应的活化能逐渐减小。与TGA相比,同一升温速率下,MFBRA中半焦气化反应的起始反应温度和最大反应速率对应的反应温度明显较小,而且升温速率越大差异越显著。无论是单一升温速率法(升温速率≥5℃·min^-1)还是组合升温速率法,TGA测得的动力学数据均明显小于MFBRA测得的动力学数据。高升温速率下(升温速率≥5℃·min^-1)半焦在TGA和MFBRA中非等温气化行为和动力学数据的差异很可能与MFBRA内较好的热量传递和受扩散的抑制作用较小有关。     

串行流化床煤气化试验

针对串行流化床煤气化技术特点,以水蒸气为气化剂,在串行流化床试验装置上进行煤气化特性的试验研究,考察了气化反应器温度、蒸汽煤比对煤气组成、热值、冷煤气效率和碳转化率的影响。结果表明,燃烧反应器内燃烧烟气不会串混至气化反应器,该煤气化技术能够稳定连续地从气化反应器获得不含N₂的高品质合成气。随着气化反应器温度的升高、蒸汽煤比的增加,煤气热值和冷煤气效率均会提高,但对碳转化率影响有所不同。在试验阶段获得的最高煤气热值为6.9 MJ•m^-3,冷煤气效率为68％,碳转化率为92％。     

Modelling and simulation of a coal gasification process in pressurized fluidized bed

A coal gasification mathematical model that can predict temperature, converted fraction and particle size distribution for solids have been developed for a high pressure fluidized bed. For gases in both emulsion and bubble phase, it can predict temperature profiles, gas composition, velocities and other fluid-dynamic parameters. In the feed zone, it could be considered a Gaussian distribution or any other distribution for the solid particle size. Experimental data from literature have been used to validate the model. Finally, the model can be used to optimize the gasification process changing several parameters, such as excess of air, particle size distribution, coal type and reactor geometry.     

微型流化床反应动力学分析仪的研制与应用

本文首次研发了一种用于测定气固反应速度、求算反应动力学参数的微型流化床反应分析仪器（MFBK）。该仪器利用流化床强化反应过程的热量与质量传递过程,通过气体脉冲输送在给定温度下瞬时进样,根据在线监测的气体组分浓度变化,测试反应速度、推导反应动力学参数和分析反应机理。利用该仪器测定氩气气氛中碳酸钙的分解反应表明：其表观活化能与指前因子分别为142.73kJ.mol^-1和399777s^-1,活化能在文献报道范围之内,且小于热重分析仪测定的184.3kJ.mol^-1,并建立了反应模式函数f(α)=(1-α)0.86,对应的拟合线性相关系数达到0.99。测定煤和生物质热解反应过程表明：MFBK测试的反应完成时间在15s左右,且揭示了生成气关键组分具有不同的释放时间和生成量,为深入探讨热解反应机理提供了新的证据。     

灰熔聚粉煤气化技术运行中出现的问题及措施

灰熔聚循环流化床粉煤气化技术是我国具有自主知识产权的新型煤气化技术。介绍了该技术的特点、工艺流程,总结了在应用中出现的问题及一些整改措施。     

A mathematical model of fluidized bed biomass gasification

A mathematical model of biomass gasification in a fluidized bed has been developed. It considers axial variations of concentrations and temperature in the bubble and emulsion phases. The mass balance involves instantaneous oxidation and equilibrium devolatilization of the biomass, kinetics of solid-gas gasification reactions as well as of gaseous phase reactions and interphase mass transfer and gas convection. The energy balance is solved locally for each vertical volume element, and globally on the reactor by iteration on the temperature at the bottom of the bed. Three parameters have been adjusted based on the experimental results: the heat transfer coefficient at the wall, the weighting of the kinetics of the water-gas shift reaction and the fraction of biomass carbon remaining as char after devolatilization. The model is used to simulate a pilot scale (50 kg/h) biomass gasifier, and its predictions compared to experimental measurements. The temperature and gaseous concentrations are estimated with good accuracy for the experiments using a wood feedstock, except for the concentration of hydrogen which is overestimated.     

Modeling and simulation of biomass air-steam gasification in a fluidized bed

By considering the features of fluidized-bed reactors and the kinetic mechanism of biomass gasification, a steady-state, isothermal, one-dimensional and two-phase mathematical model of biomass gasification kinetics in bubbling fluidized beds was developed. The model assumes the existence of two phases — a bubble and an emulsion phase — with chemical reactions occurring in both phases. The axial gas dispersion in the two phases is accounted for and the pyrolysis of biomass is taken to be instantaneous. The char and gas species CO, CO₂, H₂, H₂O, CH₄ and 8 chemical reactions are included in the model. The mathematical model belongs to a typical boundary value problem of ordinary differential equations and its solution is obtained by a Matlab program. Utilizing wood powder as the feedstock, the calculated data show satisfactory agreement with experimental results and proves the effectiveness and reliability of the model. __________ Translated from Chemical Engineering (China), 2007, 35(10): 23–26 [译自: 化学工程]     

生物质流化床空气-水蒸气气化模型研究

根据流化床反应器特点,结合生物质气化动力学反应机理,建立了生物质在流化床内气化的等温稳态、一维二相动力学模型。该模型所做的主要假定如下:流化床分为气泡相和乳相,在气泡相和乳相内均存在化学反应,考虑二相内的轴向气体扩散,生物质热解过程瞬时完成,主要考虑焦碳以及CO,CO2,H2,H2O,CH4等在流化床内发生的8个主要化学反应。数学模型属于常微分方程组边值问题,利用数值计算软件M atlab7.0进行编程求解。以木粉为原料,将模型结果与实验结果进行了对比,模拟结果与试验数据符合良好,在一定程度上证明了模型的有效性和可靠性。     

Modelling fast pyrolysis of biomass in a fluidized bed reactor

A compartmental one-dimensional model of a fluidized bed pyrolytic converter of biomass is presented. Reference conditions are those of non-catalytic fast pyrolysis of biomass in a shallow fluidized bed with external regeneration of the bed material. The fate of biomass and of the resulting char has been modelled by considering elutriation of biomass and char particles, char attrition as well as bed drain/regeneration. The course of primary and secondary pyrolitic reactions is modelled according to a semi-lumped reaction network using well-established kinetic parameters taken from the literature. A specific focus of the present study is the role of the heterogeneous volatile–char secondary reactions, whose rate has been modelled by borrowing a kinetic expression from the neighbouring area of tar adsorption/decomposition over char. The results of computations highlight the relevance of heterogeneous volatile–char secondary reactions and of the closely associated control of char loading in the bed. The sensitivity of the reactor performance to char elutriation and attrition, to proper management of bed drain/regeneration, and to control of gas phase backmixing is demonstrated. Model results provide useful guidelines for optimal design and control of fluidized bed pyrolyzers and pinpoint future research priorities.     

微型流化床中生物质半焦水蒸气气化反应特性及动力学研究

利用微型流化床反应分析仪考察了1123~1223 K及10%~40%蒸汽分压(SP)条件下生物质半焦-水蒸气气化的反应特性并计算动力学。结果表明：升高温度和SP有利于缩短反应时间,提高产物(H₂、CO和CO₂)生成率及总C转化率。低温(1123 K)下,反应受SP影响较大,以H₂最为明显,增幅达1.97倍;在1223 K、SP≥20%条件下,因受活性位点制约,SP对反应影响较小。随温度升高,CO/CO₂体积产率比呈现出先减小后增大趋势;在1123 K和1173 K下,随SP升高,CO/CO₂的体积产率比值降低;在1223 K下,该值维持在1.25左右。采用缩核模型求取不同SP下总碳转化活化能(E_a)在71.29~76.78 kJ/mol范围内,H₂、CO₂和CO的生成活化能分别在95.44~101.82、83.56~89.35和70.41~74.86 kJ/mol之间。测试结果弥补了现有分析仪难以测定气化过程中气体产物生成特性和动力学的局限性。     

Coal gasification in a jet-spouted bed

Coal gasification has been studied for the production of synthesis gas by use of a laboratory-scale, two-stage, jet-spouted bed reactor. Tests were conducted in the dry ash mode with oxygen-steam mixtures. The effects of operating conditions on the gasification performance were investigated at atmospheric pressure and temperatures up to 1150°C. Carbon conversions of 75% to 97% and cold gas thermal efficiencies of 62 to 78% were obtained for Taiheiyo coal. Both the carbon conversion and thermal efficiency were mainly affected by the oxygen/coal ratio. The product gases contained 36-41% hydrogen and 30-43% carbon monoxide.     

生物质流化床快速裂解模型

研究了流化床内的生物质快速裂解模型,其特点是考虑了原料粒子在下部密相区和上部稀相区的不同反应历程.模型的计算结果表明,原料粒子和产物气体在反应器内的停留时间有较大的区别,其变化情况对裂解产物的分布有很大影响.由该模型得到的计算结果能和实验值很好吻合,表明它能较好地描述流化床反应器内生物质快速裂解的反应过程.结合计算数据对影响裂解结果的一些因素进行了分析.     

Experimental study on catalytic steam gasification of natural coke in a fluidized bed

The gasification characteristics of natural coke from Peicheng mine with steam were investigated in a fluidized bed reactor. The effects of catalyst type, composition and dosage of catalyst on the yield, components and heating value of product gas, and carbon conversion rate were examined. The results show that fluidized bed gasification technology is an effective way to gasify natural coke. Also the results indicate that individual addition of K-, Ca-, Fe-, Ni-based catalyst effectively increases the gasification reaction rate of the natural coke samples. With the increase in catalyst dosage, the yield and heating value of product gas per hour increase obviously, and carbon conversion rate is improved substantially. Each of aforementioned catalysts has similar catalytic effect and trend, among which the effect of Ca-based catalyst is a little weaker. The optimum metal atom ratio of mixed catalyst is Fe/Ni/others = 35/55/10, and the mixed catalyst displays maximum catalytic performance when the catalyst dosage in the natural coke is about 4%. The experimental findings provide an interesting reference for large-scale development and utilization of natural coke.     

新型流化床粉煤多元气化制合成气技术及应用

介绍了灰粘聚循环流化床粉煤气化的原理、工艺流程及工艺特点。该流化床底部设置了灰粘聚分离装置,在炉内形成中心高温区,使炉渣在中心高温区内粘聚成灰球,借助密度差异,有选择地使煤粉与灰球分离,从而降低灰渣的含碳量,提高了煤中碳的转化率。将该技术应用于合成氨生产中,每吨氨可增加综合经济效益295 14元。     

Nickel-catalysed gasification of brown coal in a fluidized bed reactor at atmospheric pressure

Pyrolysis and steam gasification of nickel-loaded Yallourn coal were carried out in a fluidized bed reactor at ambient pressure. The pyrolysis mode was influenced by the addition of nickel catalyst. The yield of total volatile matter decreased whereas the gas yield markedly increased, when compared with uncatalysed pyrolysis. This is considered to result from tar decomposing on the catalyst and being converted to gases and deposited carbon. For the catalysed steam gasification, ≈ 80 wt% of coal conversion was achieved at 873 K and the gas yield was twelve times as much as that for the uncatalysed reaction. The homogeneous equilibrium in the gas phase controlled the composition of the product gas. The product gas contained little tarry material and a negligible amount of hydrogen sulphide. Nickel was efficiently recovered from the residue by an ammonia-leaching method.     

Oxygen-steam gasification of coals in a spouted bed

A bituminous and a sub-bituminous coal from Western Canada have been gasified in oxygen-steam and air-steam mixtures in a 0.30-m diameter, 50 kg coal/h continuous spouted bed reactor. Results are presented to show the effects of the blast composition and reactor temperature on gas heating value and carbon conversion. Operation in the ash agglomeration mode is illustrated, and the role of K₂CO₃ as catalyst explored. Results from a wide range of experimental gasification conditions are compared with predictions of an equilibrium model.     

循环流化床煤燃烧/热解双反应器系统稳定性分析

为了考察循环流化床煤燃烧/热解双反应器系统的稳定性,在冷态实验装置上以电厂锅炉灰为实验物料,其中提升管的内径为100 mm,高为6.7 m,与热解室相连立管的内径为44 mm,高3 m,热解室的截面积为200 mm×200 mm,高770 mm。分别考察了影响系统稳定运行的主要因素,并对系统中存在的几对平衡关系进行了分析。结果表明,旋风料腿内的固体料位高度、热解室内的料位高度以及热解室内的压力等是影响系统稳定运行的关键因素,尤其是热解室内压力的增加有可能使立管内料封破坏,最终导致系统瘫痪。而提升管与热解室立管之间压力的平衡以及提升管与旋风分离器料腿之间压力的平衡等在操作过程中必须保持稳定,否则也会发生窜气、架料、旋风分离器效率下降等现象,影响系统稳定运行。     

流化床粉煤气体热载体快速热解反应器的计算

在冷态模拟实验和煤热解动力学计算的基础上,对粉煤气体热载体快速热解提升管反应器的高度进行了计算。利用高速摄像粒子测速法结合互相关算法研究了不同气体流量和不同颗粒粒径时固体颗粒在热解提升管中的运动速度,通过求解神府煤热解动力学方程,得到了不同粒径神府煤颗粒热解挥发分析出的时间,从而确定了快速热解提升管反应器的高度。研究结果表明:当气体流量在850 m3/h,粉煤的粒径主要集中在0.7—3.0 mm时,提升管的高度应选择在10.0 m。